Method of making spun bond web from multicomponent filaments

ABSTRACT

A spun bond mat, after collection on a perforated surface is consolidated by high velocity water jets and then subjected to heat treatment to crinkle or crimp the bicomponent or other multicomponent synthetic resin filaments.

FIELD OF THE INVENTION

[0001] My present invention relates to a method of making a spun bondweb of multicomponent filaments and, more particularly, to a method ofmaking a filament web with increased filament bulk.

BACKGROUND OF THE INVENTION

[0002] When reference is made to multicomponent filaments here, I meanfilaments which are composed of a plurality of different thermoplasticsynthetic resin components and especially components with differentproperties like thermal coefficient of expansion, heat-induced shrinkageand like properties. These components can be of the same syntheticresin, for example, poly sters of different composition or polyethylenesor polypropylenes of different properties, or components of differentsynthetic resins, like, for example, a polypropylene component and apolyethylene component. A reference to a bicomponent filament isintended to mean a filament which has only two different thermoplasticsynthetic resins.

[0003] A cross section through such filaments will show the twocomponents, usually in a side-by-side relationship and the separation btwe n the two synth tic resins gen rally will ext nd over the entirelength of the filament.

[0004] The reference to spun bond here is intended to mean webs whichare formed from continuous filaments as well as webs which may be formedfrom less than continuous filaments, i.e. filam nts which may havevarious lengths and need not be continuous.

[0005] In the usual production of spun bond, i.e. webs formed from matsof such continuous or semicontinuous filaments, the mats or fleeces havethe filaments thereof bonded together at cross-over points. One of theproperties that is generally of importance in such webs is the bulk ofthe filaments. The bulkiness property in some cases leaves much to bedesired.

[0006] In general, the filaments are extruded from a spinn ret, arestretched, generally by entrainment with air, and are collected on aforaminous surface on which the mat is formed and on which the filamentsare bonded at their crossing points.

[0007] In conventional spun bond processes, the bulkiness may not bsufficient, the mechanical properties of the web may not b satisfactoryand neither may be fully reproducible. As a consequence, in earlierprocesses, there may be an excessive r j ct rate.

OBJECTS OF THE INVENTION

[0008] It is the principal object of the present invention to provide animproved method of making a reproducible filament web with a high degreeof bulkiness and surprisingly eff ctive mechanical properties.

[0009] Another object of the invention is to provide a method of makinga filament web of high bulk, good mechanical properties and a highdegree of reproducibility without drawbacks of prior art systems.

SUMMARY OF THE INVENTION

[0010] These objects are attained, in accordance with the invention in amethod for the purposes described in which the spun bond web is madefrom multicomponent filaments whereby the multicomponent filaments aredeposited upon a collecting surface or support and the mat thus formedby collecting the multicomponent filaments is bonded together orconsolidated by a water jet system of the mat. Subsequently, a filamentcrinkling or crimping is introduced in the resulting web by a heat tratment thereof to produce a high bulk spun bond web.

[0011] More particularly, the mat may comprise

[0012] (a) extruding multicomponent filaments consisting of at least twosynthetic-resin components;

[0013] (b) depositing the multicomponent filaments in a mat upon asupport;

[0014] (c) consolidating the mat of multicomponent filaments to a web bysubjecting the mat to a water jet treatment; and

[0015] (d) heat treating the web to effect crinkling or crimping of thefilaments thereof and bulking of the web.

[0016] As previously noted, the term “filament” is here us d to refer toendless filaments of thermoplastic synthetic resins as are commonlyemployed for spun bond although it can encompass, as far as the presentinvention is concerned, also shorter filaments and fibers which canbenefit from being bonded in the w b by the application of the waterjets and crimped or crinkled by the heat treatment.

[0017] I have found that the invention is especially effective whenbicomponent filaments are used. The bicomponent filaments are comprisedof only two different thermoplastic synthetic resins with differentcharacteristics and especially different thermal expansion coefficients,different shrinkage properties and/or different mechanical or chemicalproperties in addition to th shrinkage and expansion.

[0018] The most highly preferred filaments are those which have two ormore synthetic resin components in a side-by-side structure, i.e. thetwo components run next to one another to the full length of thefilament. This applies especially to bicomponent filaments with aside-by-side structure. Along the length of the filament, a portion ofthe surface thereof is formed by the first polymer and the remainder bya second polymer in such bicomponent filaments. The use of thebicomponent filam nts in a side-by-side structure has been found toeliminate completely problems with earlier low-bulk webs and to providesurprising advantages with respect to high bulk webs.

[0019] The bicomponent filaments and, generally, multicomponentfilaments ar produced by the individual extrusion nozzle of a spinneretadapted to handle two or more synthetic resin components. The extrudedfilament can be cooled, e.g. by contact with process air in a processair shaft and can be stretched in their passage downwardly along thisshaft. The foraminous surface can be a perforated conveyor belt, i.e. asi ve belt which can be evacuated below he surface.

[0020] The water jet stabilization of the mat to produce the web canemploy a multiplicity of fine very high speed water jets dir cteduniformly over the entire mat surface. The water jets pr ss theoverlying filaments against underlying filaments to effect fusionbetween the filaments at the cross-over points.

[0021] Following the water jet treatment, the web is activated by a heattreatment and especially a heating in hot air at a temperature above 60°C. Because of different shrinkage and/or xpansion characteristics of thepolymers in the filaments, a crinkling or crimping is produced whichbulks the web. Indeed, the w b which results in accordance with theinvention has especially high bulk and optimal mechanicalcharacteristics which app ars to derive from the combination of waterjet stabilization and subsequent heat treatment. In fact, withoutmulticomponent and especially bicomponent filaments and both the waterjet stabilization and heat treatment activation, an equivalent high bulkmechanically satisfactory web is not obtainable.

[0022] It has be n found, for xample, that the inv ntion provides a w bwith esp cially long free filament segments, i.e. a high free filamentlength, in terms of the average length of filaments between two bondingor contact sizes with filaments at cross-overs. The high prefilamentlength means that the crimp, curling and in general bulking which isformed by the crinkling step, allows the development of a large numberof loops, bends and other formations which extend transversely to theweb and account for the bulk thereof. In addition, the bulking is espcially reproducible.

BRIEF DESCRIPTION OF THE DRAWING

[0023] The above and other objects, features, and advantages will becomemore readily apparent from the following description, ref rence beingmade to the accompanying drawing in which:

[0024]FIG. 1 is a diagrammatic cross section of a bicomponent filamentin accordance with the invention;

[0025]FIG. 2 is a schematic side view of the filament coll ction portionof the apparatus and the units downstream th reof in accordance with theinvention;

[0026]FIG. 3 is a diagram illustrating the water jet stage of thinvention; and

[0027]FIG. 4 is a diagram showing the hot air treatment stag.

SPECIFIC DESCRIPTION

[0028]FIG. 1 shows a cross section through a bicomponent filament inaccordance with the invention and from this Figure it can be seen thatthe bicomponent filament comprises a polymer A making up half the crosssection of the filament and a polymer B making up the other half of thecross section. The two polymers adjoin at an interface 1 a and thus arein side-by-side relationship over the length of the filament.

[0029] Of course, either one of the components A or B can mak up agreater portion of the cross section than the other and can extend overa greater portion of the surface of the filaments than the other. Thepolymers A and B are for example two polymers which are compatible withone another and bond int grally to one another but have different heatshrinkage properties or different coefficients of thermal expansion.

[0030]FIG. 2 shows in highly schematic fashion the formation of the spunbond web in accordance with the invention. The filaments 1, collectedfrom a spinneret from which the bicomponent filaments are extruded and acooling and stretching shaft (not shown), gather on the endless sievebelt 2 into a mat 5 which is displaced in the direction of the arrow C.In a stabilizing station 3, the filament mat or fleece is subjected to amultiplicity of high velocity water jets as shown at 3 a in FIG. 3,these water jets serving to bond crossing filaments 1 to one another atbonding points 1 b where these filaments cross one another. Aconsiderabl free length L may be provided between bonding points.

[0031] The water jets can be extremely fine water jets and preferablyare of very high velocity. The water jets can be directed from nozzleshaving a diameter of from several millimeters to a fraction of amillimeter and at a pressure ranging from 2 bar to 1000 bar.

[0032] Subsequently the bonded filaments of the mats which now form aweb 5 a pass into a heat-treating station 4 in which hot air can bedirected onto the web. The hot air flow is r pr sented at 4 a in FIG. 4and serves to cause crinkling or crimping at 1 c of the filaments 1between the fusion point 1 b. Th result is a high bulk spun bond web.The apparatus of FIG. 2 has been shown in a highly simplified manner. Itwill be understood that other processing elements and apparatuscomponents may be used where required or desirable.

I claim:
 1. A method of making a filament web, comprising the st ps of:(a) extruding multicomponent filaments consisting of at least twosynthetic-resin components; (b) depositing said multicomponent filamentsin a mat upon a support; (c) consolidating the mat of multicomponentfilaments to a web by subjecting said mat to a water jet treatment; and(d) heat treating said web to effect crinkling of the filam nts thereofand bulking of the web.
 2. The method defined in claim 1 wherein themulticomponent filaments produced in step (a) are bicomponent filam nts.3. The method defined in claim 2 wherein said multicomponent filamentshave the components thereof in side-by-side relationship.
 4. The methoddefined in claim 3 wherein said h at tr ating of said web in step (d) isa treatment of said web with hot air.
 5. The method defined in claim 1wherein said multicomponent filaments have the components thereof inside-by-side relationship.
 6. The method defined in claim 5 wherein saidheat treating of said web in step (d) is a treatment of said web withhot air.
 7. The method defined in claim 1 wherein said heat treating ofsaid web in step (d) is a treatment of said web with hot air.